After you've added your product inventory and options, you'll want to decide whether or not you want to track your inventory in the application (as opposed to manually or using a separate system). The benefit of tracking inventory in the application is that your product availability will update in real time as people make purchases, but if your inventory is depleted by other sources (for example, within in your physical store), you'll need to keep this in mind and update your inventory levels accordingly.

Once you're in your product editor, scroll down to the section titled "Inventory." Click the dropdown underneath "Do you want to track Quantity?" Select the track inventory option.

This will bring up inventory tracking options. Determine the appropriate amount of products you have in stock, and insert that number into the quantity field. If the product level reaches zero, you have the option of allowing customer to backorder, or suspending sale altogether. Select which option is best for you.